Straightening a blade

G

ggoose

Joined
Apr 30, 2014
Messages
139
Is there any limit to how many tempering cycles a knife may undergo? I have put a particular blade thru about 8 cycles attempting to remove a bend in the edge which occurred during heat treat (to no avail). On another note, how does one remove a particularly stubborn bend in a blade that hasn't straightened out after 8 tempering cycles...? Thus far I have (repeatedly) fastened the knife ends to a piece of angle iron with a couple of c-clamps, with a small piece of steel between the bend and the angle iron, and run thru a tempering cycle...has always worked before. The steel is cpm 3-v heated, plate quenched, sub-zeroed, and tempered and re-tempered until I became ill-tempered :mad:

Thanks in advance...

gene
 
What tempering temperature did you use ? Did you overbend for springback ? What was the dimension of the bend ?
 
Mete's questions are where you should start. My big question is how long did you temper the blade each time you tried straightening it? A few minutes isn't enough. Fifteen minutes is barely enough.....thirty is what I call the minimum.

In practicality, there is no limit on tempering cycles in the range we use for knives.

I straighten a stubborn bend/warp by heating to 400F and holding for 30 minutes. Then I remove the blade while wearing HT gloves and hand straighten the bend. If needed, I stick in a three-point jig in the vise and let it cool with the bend overcompensated.
Occasionally, I put the blade on the wooden anvil and use a wooden mallet to "hammer" out the bend/warp. All this is done above 200F. If it needs more, I stick it back for 15 minutes and do another straightening attempt. Once fully straight, I give it another 30 minute temper and water cool when done.

If a warp/twist/bend is bad or really stubborn, it may be best to completely stress relieve the blade, straighten properly on the anvil, check on the granite surface plate, and then re-do the HT.
 
Last edited:
If I have a bend, I do the first temper cycle as-is.
Clamp the blade with an appropriate over-bend at the apex of the deviation and give it the full second temper. I might add 20 minutes or so to compensate for the extra mass of the clamp and bar for everything to get up to heat.
I fully quench blade and clamp apparatus right out of the oven with the blade in its over-bent position.
It is very rare that I have to do a third cycle. But if I do, it is for a full hour, but sometimes I drop the temp 50 degrees and that's still plenty of heat.

Just a bit off topic, but make sure your oven is at full temp for a good 1/2 hour before putting your knife in. And allow a good 20 minutes for your blade to get up to oven temp before beginning countdown.
If I require a full 1 hour tempering time, I place the blade in a pre-heated oven for a full 1.5 hours.
 
What was the process you used to harden the CPM-3V? (plates, air, oil)
Sometimes, I'll get a bad quench and try to fool myself into thinking I didn't. The first sign for me is a warped blade. The second sign is a warp that won't go away. Odds are at this point, even if you manage to get the warp out it'll rear it's ugly head during the finishing. If it won't come out in the temper, I suck it up and heat treat again.
 
Thanks for the replies.

Mete: I tempered at 400 degrees F for 1.5 - 2 hrs each time; every time it didn't work, I over-bent more, but without luck.

Stacy: I don't have a 3-point jig beyond the c-clamps and angle iron; I'll have to look into that. My tempering cycles were at or near full duration, as mentioned above. I will try the hammer/wood anvil approach as it sounds therapeutic.

Karl: When you fully quench the blade and apparatus out of the oven, how so? Just a water quench? I was letting it air cool in the over bent configuration.

Rick: The blade was plate quenched; the re-heat treat is now on the list of things to do if I don't figure this out soon.

I have an image but I don't think my membership level allows me to post it in attachment form...
 
ggoose said:
Karl: When you fully quench the blade and apparatus out of the oven, how so? Just a water quench? I was letting it air cool in the over bent configuration.
Click to expand...

I have large quench tanks so I just quench the whole mess in my oil.
I do this on the first cycle even when a knife is perfectly straight.
That way you can go immediately to your second temper cycle.
A Kevin Cashen tip.

And I'll say this - I don't get upset about a little warp. That tells me I got stuff HARD!!! It's when a knife stays perfectly straight that I get a little concerned. I'm happy when it does, but I take steps to ensure that cutting edge did what I wanted it to.
 
Karl B. Andersen said:
I have large quench tanks so I just quench the whole mess in my oil.
I do this on the first cycle even when a knife is perfectly straight.
That way you can go immediately to your second temper cycle.
A Kevin Cashen tip.

And I'll say this - I don't get upset about a little warp. That tells me I got stuff HARD!!! It's when a knife stays perfectly straight that I get a little concerned. I'm happy when it does, but I take steps to ensure that cutting edge did what I wanted it to.
Click to expand...

Thanks for the Kevin Cashen tip...I do have a big pot of canola for quenching. I'll try it on my next heat treat.
 
You can quench them it water, right out of the temper. It actually improves the blade in some metallurgical way. I've read the info Roman Landes put up many times and know it helps prevent cold embrittlement... but don't ask me to explain.:o
 
You must log in or register to reply here.
Back
Top